Metal speciation and leachability of heavy metals from Enersludge™ ash in concrete

The Oil From Sludge (Enersludge™) process converts sewage sludge into hydrocarbons, partially fixing heavy metals in the by-product ash. Research was carried out to investigate the speciation and leaching behaviour of heavy metals (cadmium, copper, chromium, nickel, lead and zinc) when using this ash product in concrete. This was achieved by conducting a sequential extraction procedure, a soluble fraction test and dynamic leach test. Sequentialextraction showed that heavy metals in the ash speciated mainly into a stable form. Leachable heavy metals were derived mainly from the concrete (control samples). The soluble fraction test and the dynamic leach test indicated that heavy metals from concrete with Oil From Sludge ash addition exhibited a low leachability.